1. Field of the Invention
The present invention relates to an electric motor, and more specifically to a fan apparatus having the electric motor.
2. Description of the Related Art
Conventionally, some motors in fan apparatuses are constructed such that a rotor portion is attracted to a stator portion by using a magnetic attractive force in order to restrict rising of the rotor portion and an impeller relative to the stator portion during rotation. In such an arrangement, the motor is provided with an attracting magnet which contacts a tip end of a shaft or a magnetic member which faces a field magnet in a direction parallel to the center axis.
In such a motor, the magnetic member is fixed to the stator portion by various techniques. For example, in an axial fan motor disclosed in Japanese Patent Gazette No. 4005670, an annular printed wiring board is attached around a bushing into which a shaft is inserted, and an attracting member having a substantially annular shape for magnetically attracting a permanent magnet is attached on the top side (i.e., on the side toward a rotor) of the printed wiring board. A stator yoke having four standing portions which protrude upwardly from its outer circumference is further provided on the attracting member. Since these standing portions face a lower portion of the permanent magnet of the rotor in a direction perpendicular to the center axis, the permanent magnet is also attracted to the stator yoke to perform stable rotation of the rotor.
In a substantially annular-balancing portion in a motor disclosed in U.S. Pat. No. 7,221,069, an annular portion of the balancing portion is fixed around a cylindrical portion of a base into which a shaft is inserted. Four magnetic surfaces, which extend from the outer circumference of the annular portion toward a rotor, face an annular magnet of the rotor in a radial direction.
In a motor disclosed in U.S. Pat. No. 6,097,120, a balancing sheet having an opening formed in its center is attached around a cylindrical portion which is provided on an opposite end surface of a stator to a rotor. In the motor, the balancing sheet and a permanent magnet of the rotor face each other in a direction parallel to the center axis.
In another arrangement of the motor disclosed in U.S. Pat. No. 6,097,120, the balancing sheet and a core of the stator are formed as one member.
In a large-sized fan measuring 90 mm per side or the like or a fan having a high rotation speed, the magnetic attractive force generated between the magnetic member and the field magnet should be increased when compared with a small-sized fan or a fan having a low rotation speed, in order to prevent rising of the rotor portion relative to the stator portion.
However, the arrangements of the motors disclosed in Japanese Patent Gazette No. 4005670 and U.S. Pat. No. 6,097,120, are complicated or have a decreased flexibility of design of the stator to locate the magnetic member sufficiently close to the field magnet. Since a field magnet faces a magnetic member only in the direction perpendicular to the center axis, it is difficult to generate a sufficient magnetic attractive force by the magnetic member disclosed in U.S. Pat. No. 7,221,069.